ABSTRACT People suffering from anxiety disorders such as post-traumatic stress disorder (PTSD) very often use and abuse reinforcing drugs such as opioids. Although the comorbidity of PTSD and substance abuse is exceedingly high, little is known about the neurobiological mechanisms that result in this comorbidity. By leveraging the Fanselow laboratory's development of a preclinical model of PTSD with the expertise within the Center for Study of Opioid Receptors and Drugs of Abuse (CSORDA) we plan to attack this question. Based on findings with our model we hypothesize that, during a single traumatic event, stress hormones (corticosterone/cortisol) and neuromodulators (acetylcholine) act in concert on amygdala neurons resulting in changes in neural plasticity within this brain structure. These changes result in the altered fear responses that characterize several aspects of PTSD. The amygdala also contains neurons that participate in the rewarding property of drugs and we hypothesize that trauma causes similar changes in those neurons and this leads to increased drug reward learning. Therefore, in Aim 1 of this proposal we will determine if manipulations that mitigate the potentiation of fear learning caused by trauma also mitigate alterations in drug responsivity following trauma. Aim 2 seeks to identify a set of amygdala neurons that are activated by BOTH trauma and drug exposure and using optogenetics tests if activity in these neurons is necessary for comorbidity. We will also assess how stress and drug experience alter gene expression patterns in the amygdala. While most of the focus on drug use/anxiety disorder comorbidity has focused on stress as a causal factor in altered drug taking, we have obtained preliminary data that the converse is also true. A history of drug use and withdrawal increases the impact that a future stressor has on fear processes. Aim 3 investigates potential mechanisms for the ability of drug exposure to adversely impact fear behavior. We will determine if mu-opioid or kappa-opioid receptors in the amygdala are necessary for morphine's effects on future stress reactivity. We will also use resting state fMRI, with an amygdala seed, to determine the overlap in the modifications of whole brain connectivity caused by drug exposure and by stress.